BNW log BNW log

Bats Northwest

"helping bats in Washington State"

The Western Long-eared Myotis (Myotis evotis)

The Myotis or mouse-eared bats are a genus of small, plain brown bats and include the most common and numerous species in the country. In Washington there are seven different kinds, many of which are quite similar in both looks and echolocation calls. But if you ever see a Long-eared Myotis up close, you'll have little doubt what you're dealing with.1

It's not that their ears are huge like the Spotted Bat or even the Townsend's Big-eared Bat. It's just that they are huge for a Myotis. M. evotis has ears that can run more than 3/4 of an inch! A common trick of researchers is to press the ear of a Myotis forward over the face and see how far beyond the nose it extends. In some species, it doesn't even reach the end of the nose. But the ear of this bat can go more than 1/4 inch past it.

Why such long ears? Scientists usually say that this attribute relates to hunting style. Many large-eared bats, including M. evotis, are known as gleaners because these extra-big listening devices can pick up the slight noises of beetles, flies and spiders moving around on leaves. This bat will often approach an insect without echolocating and just listen for telltales noises, then snatch or "glean" the insect from the surface its sitting or crawling on. In fact, even the fluttering of moth wings can be heard by M. evotis, and moths make up a major part of its prey. Still it is quite capable of catching small insects on the wing.

The Long-eared Myotis's echolocation call is different from the average Myotis too. It is short, quiet and very high pitched - all adaptations for a cluttered environment such as a forest. But this species is actually found in a wide range of habitats from arid grasslands to moist coastal forests. Perhaps because it is such a generalist in its eating habits, reproductive females are able to live at fairly high altitudes where flying insects are not as abundant.

Apparently these bats use mines only as night roosts. During the day, Long-eared Myotis may roost under bark, in rock crevices and hollow trees. The females will form small maternity colonies and seem to prefer buildings during this time. It has been noted that occasionally a male will join the colony. But in general, little is known about the behavior and biology of this species. There is no information on hibernation sites for M. evotis.

Myotis evotis appears to be widespread throughout the western states, but not abundant. The preference for warm attics during the birthing season puts them at some risk. Of two maternity colonies I have personally dealt with in the Puget Sound region, only one is being protected by the kind homeowner. Because we lack adequate information on both behavior and populations, many states including ours have made these bats a 'Species of Concern'. This 'pretty little bat', as Barbour and Davis2 called it, definitely is in need of further study.

Notes

  1. Researchers are currently studying how to distinguish the widespread though uncommon Long-eared Myotis (Myotis evotis) from the nearly identical but very rare Keen's Myotis (Myotis keenii).
  2. Barbour and Davis. 1969. Bats of America. University Press of Kentucky.